1. Field of the Invention
The present invention relates to an image formation apparatus employing an electrostatic recording method, and in particular to a wet-type image formation apparatus equipped with belt-shaped photoconductor.
2. Discussion of Background
In an image formation apparatus employing an electrostatic recording method, such as a plain paper copier (PPC), a powdered developer is generally used for developing a latent electrostatic image into a visible toner image.
A liquid-type developer is also conventionally used in this kind of image formation apparatus. This wet development process is superior to the above-mentioned dry-type development process in the image quality of the obtained images because of the difference in the diameter of the particles constituting the developer. The wet development process, however, has a shortcoming inasmuch as the handling of the image formation apparatus is troublesome.
To achieve the image formation in this kind of image formation apparatus a drum-shaped photoconductor is usually used. In the case where the drum-shaped photoconductor is employed, however, the focus on the outer surface of the drum-shaped photoconductor may deviate when the drum-shaped photoconductor is exposed to light images which are converted from original images by an optical scanning system. In addition, flash exposure cannot be used, so that the high-speed image formation cannot be obtained. Furthermore, compact image formation apparatus equipped with a drum-shaped photoconductor is difficult to fabricate.
To solve the above-mentioned problems, a belt-shaped instead of a drum-shaped photoconductor has been used in a dry-type image formation apparatus.
However, the aforementioned belt-shaped photoconductor cannot be employed in the wet-type image formation apparatus because of various problems caused by the use of the liquid developer. For example, the belt-shaped photoconductor slips from the pulleys because the liquid developer flows into the gap between each pulley and the belt-shaped photoconductor. In addition to the above, the liquid developer drops onto the image transfer unit along the inner surface of the belt-shaped photoconductor, and the transfer sheet is therefore stained with the liquid developer in the image transfer unit. This problem frequently occurs when the carrier liquid for the liquid developer contains silicone oil which evaporates relatively slowly.
Furthermore, toner particles contained in the liquid developer are deposited in the areas around the belt-shaped photoconductor if the image forming operation is discontinued for a long time, because the carrier liquid for the liquid developer readily evaporates. For these reasons, the belt-shaped photoconductor is conventionally used only in the dry-type image formation apparatus.